1. Field of the Invention
This invention relates to valves with improved sealing properties, particularly to valves for high-pressure of high-vacuum applications for which improved sealing is an important property.
2. FIG. 1--Description of Prior Art
Valves for high-vacuum or high-pressure applications are widely used in various fields of industry. For example, valves used in the manufacture of semiconductors must withstand a vacuum as low as 10.sup.-14 torr (torr=0.01216 atmosphere), while valves employed in pneumatic or hydraulic systems may work under pressures exceeding 100 kg/cm.sup.2.
One existing valve, which is intended for high-vacuum applications and is produced by Huntington Laboratories, Inc., Mountain View, Calif., is shown in FIG. 1. It consists of a valve housing 10 which has an inlet pipe 12 with an inlet mounting flange 14 and an outlet pipe 16 with an outlet mounting flange 18. On the side opposite to outlet pipe 16, the housing is closed by a cover 20 which rests on a cover flange 22. A copper, annular seal 24 is placed between the mating surfaces of cover 20 and its flange 22. Cover 20 and its flange 22 are tightened together by bolts 26 which pass through holes 28 in cover 20 and are screwed into threaded holes 30 in cover flange 22. Bolts 26 are tightened so that the interface between cover 20 and flange 22 is reliably sealed.
Cover 20 has a central threaded opening 32. A threaded portion 34 of a valve stem 36 is screwed into opening 32. The lower end of stem 36 is located inside valve body 10 and carries a valve head 38 which bears a copper gasket 40. The latter is replaceable and attached, for example, by a screw 42.
The upper part of valve stem 36 protrudes outside the valve and carries a handle or an actuator 44 which can be attached to stem 36, e.g, by a screw 46.
Above outlet pipe 16, valve housing 10 has a valve seat 48 which cooperates with copper gasket 38.
For sealing the threaed connection between the stem's threads 34 and opening 32, a cylindrical bellows 50 is placed inside valve housing 10 around valve stem 36 between cover 20 and valve head 38. Bellows 50 is welded at its upper end to cover 20, forming a sealed weld seam 51, and at its lower end to valve head 38, forming a sealed welded seam 53.
In order to allow rotation of valve stem 36 with respect to valve head 38 and at the same time to fix both parts in the axial direction, valve stem 36 has, at its lower end, a collar 37 which is fitted rotatably in a recess 39 of valve head 38. Axial fixation is provided by means of a flanged edge 41 formed on the lower end of bellows 50. This flanged edge overlaps a portion of collar 37 to form a sliding-type thrust bearing. The bearing can be replaced by a thrust-type ball bearing.
For vacuum application, all parts of the valve (except for copper seal and gasket) are usually made of stainless steel.